The present invention relates to a golf club head having a hollow structure. More specifically, the invention relates to a golf club head capable of setting an optional spin characteristic of a ball without giving any substantial effects on a center of gravity or a total weight, and thereby satisfying a request made by a golfer.
The golf club head generates rotation around its center of gravity when it hits a ball by a portion shifted from a sweet spot, and then gives a spin to the ball. This spin generating mechanism is generally called a gear effect. For example, in a conventional head structure, because of the gear effect, the quantity of backspin is reduced more for a ball hit by a head upper portion compared with a ball hit by a center portion. The quantity of backspin is increased more for a ball hit by a head lower portion compared with a ball hit by a center portion. In the case of a ball hit by a head toe portion, hook rotation (left rotation) is generated and, in the case of a ball hit by a heel portion, slice rotation (right rotation) is generated. In addition, it is generally known that the gear effect is increased as a thickness of a face portion is thinner, and the gear effect is reduced as a thickness thereof is thicker.
Thus, to control a spin characteristic of a ball, efforts have been made to reduce the gear effect by changing the thickness of the face portion to change its rigidity. However, the changed thickness of the face portion resulted not only in the change in the rigidity of the face portion but also in the change in the center of gravity or total weight of the golf club head. Moreover, the changed thickness of the face portion resulted in the complexity of designing a core used for molding. Consequently, thickness accuracy was difficult to obtain, and a molten metal flow failure and other manufacturing difficulties easily occurred. The changed thickness also caused inconveniences such as a deteriorated hitting sound as a golf club head.